longer stroke engine can be narrower?

[shoatx]

I am trying to decide which way i want to go on my next engine build, and have read many posts on here about the pros and cons of different strokes.
What i cant seem to comprehend is how can an engine with a 78 or 82mm stroke be stock width or narrower than a 74 or 76mm stroke? And why does it take less case clearancing with a shorter stroke than a longer stroke?
I also really don't understand how you know which rod length to use with which stroke and why.
Can some of you more experienced engine builders guide me in the right direction?
Thanks for the help

Randy
_________________
1957 Beetle Currently under restoration.
1974 std. Beetle
Sand rail buggy.

[stealth67vw]

My 78 x 94 engine with 5.352 rods is more than an 1/8th inch narrower than a stock 1600. it actually made the tin hard to fit in the opposite direction than a normal stroker engine.
_________________
John Bates
JB Machining Services
1967 street Bug 2276 w/ 48 IDAs, 2050lbs with driver
7.76 @ 89.55mph 1/8 mile
12.27 @ 109.56 mph 1/4 mile

https://youtube.com/shorts/GmifEu5QvnA?si=OIw8eM7QU3LMhtiz
https://www.tiktok.com/t/ZT68foYFS/

[modok]

If the distance from the piston pin to the top of the piston is made shorter, this allows more stroke. Stock is 39.6, if you get a b piston with 35mm pin height, then that is approx 4.5mm shorter, which lets you fit 9mm more stroke, or 78 stroke

that is how it works

[Ian Godfrey]

5 things determine width: stroke, rod length, piston pin height, deck and head flycut. So mix and match standard products or get custom pistons.
Eg. I have a 86 crank, 5.5 rods, .45 deck, no flycut with custom JE pistons to get stock width.

[Eaallred]

82 stroke, B pistons, .043" deck, flycut heads.

My 2276 is 7/6" narrower than a stock 1600.
_________________
Eric Allred

You have to remember something: Everybody pities the weak; Jealousy you have to earn.

[[email protected]]

told you that you should have used an 84 or 86 crank!!!!

[mark tucker]

[[email protected]]

Pistons are made in different versions, with different pin heights. "A" Pistons are for 69mm stroke and 5.4" long rods. "B" Pistons are for 82mm stroke and 5.4" rods. All else the same, these engines will be the same width.

Things change when you use a different length connecting rod. Longer = Wider.

Lower Compression Ratios will result in WIDER engines, since they usually have bigger deck heights. Also, Lower CR engines has heads that are NOT flycut, so they are wider than higher compression engines that have had the heads flycut.

Sometimes I have customers that are building an engine, and they reach a point where the engine is too wide. SOMETIMES you can make it narrower by changing to a bigger camshaft. This is because with a bigger cam, you need more compression for it to work, so the customer ends up reducing deck height, and/or fly cutting the heads, both of which narrow the engine.

This is why I state that a 2275 is easier to build than a 2007 or 2165; the 78mm crank results in too much deck, which you then have to work around to "fix". It's easy-cheesy with the 82 stroke, B pistons, and 5.4" rods. No "fixing" needed.

If you are using a "healthy" compression (Over 9:1), an 84 stroke engine will be stock width, or even slightly narrower, depending if you use 5.4 or 5.325" rods. When you start running 5.5 and longer rods the engine gets wider.

The "Middle Strokes" of 74-78mm take more work, and wind up not quite a "Bolt together" package, with minor shimming or rod length changes to fix.
_________________
It's just advice, do whatever you want with it!

Please do NOT send me Private Messages through the Samba PM System (I will not see them). Send me an e-mail to john at aircooled dot net

"Like" our Facebook page at
http://www.facebook.com/vwpartsaircoolednet
and get a 5% off code for use on one order for VW Parts ON OUR PARTS STORE WEBSITE, vwparts.aircooled.net

[shoatx]

Thanks all, i think it is getting clearer now. John, what would determine which rod length i would use? just how much deck height i ended up with when mocking it up or what? How do you know which length would be best?

Randy
_________________
1957 Beetle Currently under restoration.
1974 std. Beetle
Sand rail buggy.